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Q&A Spotlight

Are Structural Insulated Panels the Right Choice?

A homeowner gets conflicting advice on the merits of building with SIPs

A timber frame gets its insulation on the outside. One approach is to wrap the frame in structural insulated panels. Another is to frame exterior walls conventionally with dimensional lumber. A GBA reader planning a house in Colorado wants to know which method is best. Photo courtesy Alison Steele-Myers.

Lynne Mc and her husband are in the process of building a timber-frame home in Colorado—elevation 7500 ft.—and have run into a snag on what kind of exterior wall and roof assembly would be best.

The timber frame manufacturer suggests that the exterior of the house be wrapped in structural insulated panels (SIPs), which are assemblies that include interior and exterior surfaces, plus a layer of insulating foam in the middle. Building conventionally framed walls around a timber frame is inherently more costly, the manufacturer argues, so why not pay a small additional upcharge and get SIPs?

“Our builder recommends the exact opposite,” Lynne writes in this recent Q&A post. “He would prefer to build 2×6 framed walls with blown-in cellulose insulation and use a SIP ‘hot-roof’ system. He feels the climate and energy costs don’t justify the expense of SIP walls, nor any other form of advanced energy design or exterior foam.”

One wrinkle is how the roof overhangs will be handled. One option is to extend interior beams to the outside to support their weight, requiring added effort for insulating and sealing, Lynne says. Or, timbers could be terminated at the wall line with exterior brackets added to support the roof overhangs. With a SIP roof, she adds, this complication disappears because the panels are self-supporting. The SIP roof, however, is more expensive, and eats up money that Lynne and her husband were hoping to use for upgraded windows.

“We are very anxious to hear the recommendations of the GBA community and look forward to your feedback,” Lynne says. “Which of the options above would you recommend, or is there a better alternative? Although we are committed to being energy-efficient, we are limited by budget, and worried about future disasters caused by inexperienced workers, but…

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3 Comments

  1. CarsonB | | #1

    Scott, do you know why Benson, one of the biggest early proponents of SIPs with timberframes to my knowledge, went from using foam core SIPs to cellulose stick framed panels? Resiliency? Cost? Less GWP? Ease of modification? All of those? I do see they have one line of foam core panels as an option, but only for the roof.

  2. James Howison | | #2

    Embodied carbon of foam-based SIPs has to be higher, no? Seems that should get a look in in the discussion here.

  3. User avater GBA Editor
    Scott Gibson | | #3

    CarsonB,

    I'm sorry not to know the answer to your question. But it sounds like a topic worth exploring. Thanks for the heads up.

    Scott

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